Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and the ink sticks are pushed or slid along the feed channel by a feed mechanism and/or gravity toward a solid ink melting assembly. The melting assembly melts the solid ink into a liquid that is delivered to a melted ink container. The melted ink container is configured to hold a quantity of melted ink and to communicate the melted ink to one or more printhead reservoirs located proximate at least one printhead of the printer as needed. This melted ink container could be located on the melting assembly between it and the printhead(s) or could be part of the head reservoir.
In some printing systems, the remote ink containers are configured to communicate melted phase change ink held therein to the printhead reservoirs through an ink delivery conduit or tube that extends between the ink containers and the printhead reservoir(s). The ink is transmitted through the ink delivery conduit by introducing a positive pressure in the ink container which causes the ink in the containers to enter the delivery conduit and travel to the printhead reservoir(s). Once the pressurized ink reaches the printhead reservoir, it is typically passed through a filter before reaching an on-board chamber or tank where the ink is held and delivered as needed to the ink jets of the printhead.
One difficulty faced in using pressurized ink delivery to communicate melted phase change ink to the printhead reservoirs is foam formation in the printhead reservoirs. For example, when the printer is turned off or enters a sleep mode, the molten ink that remains in the ink containers, conduits, and printhead reservoirs can solidify, or freeze. When the printer is subsequently powered back on or wakes from the sleep mode, air that was once in solution in the ink can come out of solution to form air bubbles or air pockets in the ink containers, conduits, and printhead reservoirs. During pressurized ink delivery, air trapped in the ink containers, conduits, and printhead reservoirs may be forced through printhead reservoir filters along with molten ink creating foam. The foam poses three problems: 1) it can completely fill the volume above the nominal maxim liquid ink level in the on-board ink tanks of the printhead and lead to color mixing and/or clogged vent lines, 2) it can create a false “full” reading at the level sense probes because it occupies a larger volume than liquid ink, and 3) it can potentially become entrained in the ink flow path to the ink jets and cause ink jetting malfunction, typically termed Intermittent Weak and Missing jets (IWM's).